This invention relates to valves of the type having a valve stem and particularly to the sealing of the stem to the sleeve or passage in which it moves.
A valve stem may have a turning or sliding movement within its sleeve to open or close the valvexe2x80x94or a combination of both movementsxe2x80x94and the sealing of the stem must be adequate to contend with that movement whilst ensuring maintenance of fluid tightness against the pressure of fluid in the valve. A widely used type of stem sealing is a compression packing in which a gland, which may be bolted or threaded, applies a compressive force to a soft compression packing in a stuffer box surrounding a portion of the length of the stem. The resulting radial pressure of the packing onto the stem provides the desired seal so long as the radial pressure exceeds the pressure of fluid in the valve.
Compression may be applied to the packing by means of packing bolts which are each attached at one end to a clamp around the valve body and at their other end to a spigot, a flange or other projection bearing on, integral with or attached to the gland or sleeve which bears onto the packing. Tightening of the bolts, therefore, increases the pressure on the packing and thereby provides the radial pressure onto the stem.
It is also known to attach a spring between the nut used to tighten the bolt and the surface of the spigot or flange. Although coil springs could be used, it is conventional practice to use so-called Belleville springs which are essentially formed as a series of dished washers. Such springs have a higher compression rating than a simple coil spring. The use of these springs provides a xe2x80x9clive-loadedxe2x80x9d packing which can automatically compensate for changes that may take place in the packing under operating conditions of the valve, for example high pressures and temperatures. The volume of the packing material may reduce under operating conditions and, whereas this could harmfully effect the sealing of the stem in an unsprung valve, the spring pressure will compensate for this reduction and maintain required pressure. Alternatively, if the packing volume increases, which can happen with certain packing materials, the radial pressure on the stem in an unsprung valve could increase too much and possibly cause sticking of the stem. The spring valve, however, can accommodate the pressure increase by means of further compression of the springs.
Thus, the xe2x80x9clive-loadedxe2x80x9d packing construction can provide a useful amount of self-adjustment to maintain the correct pressure through the packing onto the valve stem.
However, conventional xe2x80x9clive-loadedxe2x80x9d packing constructions have disadvantages in that they require the provision of longer bolts than would otherwise be required in order to accommodate the springs and they require sufficient clearance beyond the spigot or gland flange to accommodate the longer bolts and the springs. In particular this may cause difficulties in fitting a xe2x80x9clive-loadedxe2x80x9d packing construction to existing valves.
It is, therefore, an object of the present invention to provide an improved xe2x80x9clive-loadedxe2x80x9d packing construction of more compact size and not requiring extra-length bolts.
Accordingly, in one aspect, the invention provides a valve having a body defining a passage, a valve stem movable in the passage to open and close the valve, a packing surrounding a portion of the length of the valve stem, a sleeve bearing axially at one of its ends onto the packing to compress it, the sleeve carrying at its other end a spigot or flange extending radially outwardly and bolts passing through and secured to the spigot or flange adjacent one of the bolt ends, the other end of each bolt being secured to a clamp which is clamped to the valve body, the bolts and the spigot or flange providing an integral spring construction.
Preferably the spigot may be in the form of a pair of integrally-formed arms diametrically opposed across the sleeve but if it is desired to use three or more arms they should be equi-spaced around the sleeve to ensure that uniform compression is applied to the packing.
In one specific embodiment of the invention the integral spring construction is provided by one or more slots in the arms of the spigot. The or each slot preferably extends generally in the radial direction in a plane perpendicular to the axis of the sleeve and provides a recess in the arm. The arm is thereby effectively divided into branches which can be forced nearer together by means of tightening of the bolt that passes through them. The arm branches in conjunction with the bolt act as an integral spring that can accommodate changes in volume of the packing in a similar manner to that described above. In other words, when the nut is tightened on its bolt, the branches of the arm are forced to deflect towards each other, or one may deflect towards the other, thereby maintaining a stored energy load which is transmitted to the packing.
The arm branches may be substantially parallel prior to tightening the nut to force the branches nearer together to achieve the desired loading. Alternatively, the arm branches may be relatively divergent prior to tightening the nut. For example, the arm branches may diverge at an angle of 5xc2x0 or less, preferably 1xc2x0xc2x1xc2xdxc2x0 towards the free ends thereof.
In another specific embodiment of the invention the integral spring construction is provided by the bolts having one or more sinusoidal bends along their length. The bend or bends provide a xe2x80x9cspringxe2x80x9d action to the bolts whereby they can store energy under compression and thereby act to maintain compressive force on the packing, if and when its volume changes.
Preferably, means is provided to limit the stored energy load when the nut is tightened on the bolt. In this way the integral spring construction can be pre-loaded up to a predetermined limit and overloading is prevented. The limit means may comprise a stop which can be fixed to provide a set pre-load or adjustable to provide a variable pre-load.
Thus, from another aspect, the present invention provides a valve having a valve stem, and a compression and packer assembly including packing surrounding a portion of the valve stem, means for axially compressing the packing to pre-load the packing and means to limit the pre-load applied to the packing.
Where the integral spring construction is provided by slots in the arms of the spigot, the depth of a slot, i.e. the distance between the branches that it separates, may conveniently be made oversize as this may render its manufacture easier. To ensure that the correct amount of deflection of a branch towards its neighbour then occurs, one or more appropriately sized washers can be fitted around the bolt to lie between the branches and to reduce the slot depth. The maximum amount of branch deflection can thereby be accurately controlled by selectively varying the size and/or number of washers between the arm branches.
Accordingly in another aspect the invention provides a kit of parts for a valve of the type having a body defining a passage, a valve stem movable in the passage to open and close the valve, a packing surrounding a portion of the length of the valve stem and a sleeve bearing axially on the packing to compress it, the kit comprising a spigot or flange to bear against the sleeve, the spigot or flange comprising at least two arms, each arm having a radially extending slot dividing the arm into two spaced branches, each arm being bored to receive a bolt whereby the spigot or flange may be clamped to the valve, and a washer to fit over the bolt between the branches, the washer being of thickness to reduce the distance between the branches to permit a maximum predetermined deflection therebetween.
Where the integral spring construction is provided by the bolts, the extension of the bolt may be controlled by any suitable means to limit the stored energy load. For example, the bolt may have a fixed or adjustable collar providing a stop to limit the pre-load obtained when the nut is tightened.
Thus, in yet another aspect the invention provides a kit of parts for a valve of the type having a body defining a passage, a valve stem moveable in the passage to open and close the valve, a packing surrounding a portion of the length of the valve stem and a sleeve bearing axially on the packing to compress it, the kit comprising a spigot or flange to bear against the sleeve, the spigot or flange comprising at least two arms, each arm being bored to receive a bolt whereby the spigot or flange may be clamped to the valve, each bolt having an integral spring portion whereby the bolt can be stretched to control loading of the packing, and means to limit extension of the bolt to permit a maximum predetermined loading to be applied to the packing.
The packing may be any suitable or conventionally used material or construction. Thus it may be contained in a packing box surrounding the valve stem where it may be compressed axially between a portion of the valve body and a movable sleeve or gland. The packing may be in the form of a multiplicity of rings of the packing material. It may also include a lantern ring through which any leakage of fluid from the valve can be let to a safe area instead of leaking to atmosphere.
The skilled man of the art will be able to determine the required slot or xe2x80x9cspring boltxe2x80x9d dimensions for his particular requirements and a means of determining this for a slotted arm spring is outlined with reference to FIG. 9 below.